1. Field of the Invention
The present invention relates to an FM-CW radar apparatus that uses a frequency-modulated (FM) continuous wave (CW) transmit signal and, more particularly, to a transmit-receive FM-CW radar apparatus that switches between transmission and reception by time division.
2. Description of the Related Art
FM-CW radar is used as a radar system for measuring the distance, the relative velocity, etc. of a target object. As FM-CW radar can measure the distance and the relative velocity of a vehicle traveling ahead by using a simple signal processing circuit, and as its transmitter and receiver can be constructed with simple circuitry, this type of radar is used as an automotive collision avoidance radar.
There is disclosed as a transmit-receive FM radar a time-division multiplexing FM radar system that does not require the provision of a high-frequency, high-gain receiving amplifier circuit which supplies reflected FM frequencies, received via a transmit-receive common antenna, to a common mixer while amplifying the received frequencies intermittently in time division fashion (refer to Japanese Unexamined Patent Publication No. H10-90397).
There is also disclosed an FM-CW radar apparatus that subtracts FM-AM conversion noise from a beat signal thereby removing the FM-AM conversion noise before the beat signal is input to an A/D converter (refer to Japanese Unexamined Patent Publication No. 2002-189074).
There is further disclosed a transmit-receive FM-CW radar apparatus that can reduce the leakage of noise components between transmitter and receiver (refer to Japanese Unexamined Patent Publication No. 11-148972).